Ralph, can you point me in the direction of someone using a beefy solid state power amplifier that are using the Speltz zeros, so I may hear from them their opinion.
@mrdecibel Yes- talk to Steve McCormack of McCormack Audio.
Perhaps Autoformers are band aids for inefficient speakers?
No- its more for reducing the distortion of an amp driving a lower impedance. All amps make more distortion into lower impedances; the ear interprets this distortion as greater harshness and lack of detail. This is why low impedance speakers are not the best investment if you want to get the most out of your amplifier dollar investment.
By increasing the load impedance on the amp, you get smoother and more detailed sound (because distortion is reduced). You might also get less power if the amp is solid state. I see the 3dB increase in power you get with 4 Ohms with a solid state amp as a rather weak rationalization since in high end audio, its usually about the presentation rather than the sound pressure.